[pmc] rpa gc optimizations
[pmc] rpa gc optimizations

Re-enable the status from 6.11.0, not too many write barriers in
ResizablePMCArray methods. Not in shift as we only move the offset
and only when needed in resize.
But it does not give us back the lost 13% in parrot-bench, from 6.11
to 7.0.

parrot/parrot,parrot/parrot,parrot/parrot,parrot/parrot,parrot/parrot